This invention concerns a manufacturing method and an apparatus for an open type polyimide molding product, as well as a reflector substrate for use in illumination equipments comprising a molding product thereof and, more specifically, it relates to a manufacturing method and an apparatus for an open type polyimide molding product, as well as a reflector substrate for use in illumination equipments capable of molding with no scratches on the surface or uneven thickness upon molding an open type polyimide molding product from a polyimide film.
Since polyimide films are excellent in heat resistance, a self-fire extinguishability and have excellent dynamic properties, chemical properties and electrical insulation property, they have been used generally as parts for electric products and electronic products utilizing such properties. As one of application uses for electric products, there is a proposal of using them as a reflector substrate for use in illumination equipments such as head lamps of automobiles in view of their excellent heat resistance and electric insulation property, as well as reduced weight (Japanese patent application Kokai publication No. 11-273431).
By the way, the reflector for use in illumination equipments is molded from a polyimide film as a so-called open type polyimide molding product and it is necessary that the light reflection property can be accurately controlled when a metal reflection layer is vapor deposited on the surface as required characteristics. Accordingly, it is important that the open type polyimide molding product is molded with no scratches on the surface.
However, while the polyimide film is excellent in the heat resistance as described above, when it is molded by press molding using molding dies comprising a female die and a male die as in the manufacturing method disclosed in Japanese patent application Kokai publication No. 11-273431, it results in a problem of causing defects such as scratches on the surface of the molding product. Further, even when a vacuum forming method is used instead of the pressure molding method in order to suppress such scratches, it still leaves a problem that unevenness in the thickness is caused when merely molding by an existent vacuum forming method and, in an extreme case, holes are formed making it difficult to stabilize the shape of the molding product.
An object of this invention is to provide a manufacturing method and an apparatus for an open type polyimide molding product capable of reducing scratches on the surface and unevenness in the thickness.
Another object of this invention is to provide a reflector substrate for use in illumination equipments comprising an open type polyimide molding product of excellent shape stability with less scratches on the surface and unevenness in the thickness.
A method of manufacturing an open type polyimide molding product according to this invention for attaining the foregoing object comprises bringing a polyimide film into an intimate contact with a molding die having a concave molding surface so as to tightly close the open end thereof, bending to deform the polyimide film under contactless heating only by a pressure difference of gas, and depressurizing a space on the side of the molding die and pressurizing a space on the opposite side relative to the polyimide film for providing the pressure difference at least in the final stage of the bending deformation and bringing the film into an intimate contact with the concave molding surface.
As described above, since a polyimide film as the molding material is bent to deform only by the pressure difference of gas while plasticizing the film by contactless heating, no scratches are caused. Further, since the polyimide film is brought into an intimate contact with the concave molding surface of a molding die only by the pressure difference by applying depressurization on the side of the molding die and pressurization on the opposite side at least in the final stage of the bending deformation, it can be molded with no unevenness in the thickness and without causing air cavities relative to the concave molding surface.
Molding with no unevenness in the thickness and air cavities described above is enabled by applying depressurization/pressurization simultaneously on both surfaces of the polyimide film at least in the final stage of the operation for the bending deformation but it can not be attained by merely depressurizing the space on the side of the molding die or pressurizing the space on the opposite side.
More specifically, contactless heating may be applied by disposing a heating portion to a pressing die and/or a molding die and irradiating radiation heat and/or discharging a heating gas from the pressing die. Operation for depressurization and pressurization is conducted by disposing a porous metal or forming a number of pores to the concave molding surface of the molding die and the inner surface of the pressing die and conducting by way of the porous metal or the pores. Further, the shape of the polyimide film after molding is fixed by disposing a cooling portion to the molding die and/or pressing die and by the cooling effect of the cooling portion and/or releasing of the cooling gas from the pressing die.
Further, in a preferred apparatus for manufacturing an open type polyimide molding product for practicing the manufacturing method described above, a molding section is constituted with a molding die having a concave molding surface and a pressing die in press contact with an open end of the molding die, the molding die is connected with a negative pressure source and the pressing die is connected with a pressurization source. The manufacturing apparatus can be provided with a film supply mechanism for supplying and setting a polyimide film to the molding section or a molding product take out mechanism for taking out the molding product from the molding section.
The open type polyimide molding product obtained according to this invention can be utilized effectively as a reflector for use in illumination equipments such as head lamps of automobiles by disposing a reflection layer by vacuum deposition of metal.